Swanson was born and raised mostly in Palm Springs, California with a Swedish-American father and a Mexican-American mother, along with his four siblings. Swanson's father died three months after he was born, and because of his mother's heavy grieving, Swanson and his siblings were then adopted by a distant relative until his mother healed. He was raised by a religious family and spent most of his early life in church. Swanson was also home-schooled for most of his young life. However, when Swanson was 14, his adoptive parents divorced and he was returned to his mother. He then went to Cathedral City High School, along with future boxerTimothy Bradley,[4] but Swanson soon began associating himself with street gangs, and was involved in many fights. When he was still a teenager, the young Swanson and two of his friends were caught committing a house robbery which caused Swanson to be placed in a juvenile detention center. Two years after his release when he was 19 years old, Swanson was working with children who have cerebral palsy and then practicing Brazilian jiu-jitsu. He was eventually given an invitation to train with UFC fighter Joe Stevenson, which Swanson accepted and soon began his MMA career.[5]

Swanson made his WEC debut on March 24, 2007 with a victory over Tommy Lee by guillotine choke. He next defeated Micah Miller at WEC 28 via unanimous decision. Following an eleven fight winning streak, Swanson lost to former UFC lightweight champion Jens Pulver, who was making his WEC and Featherweight debut. Swanson was forced to tap out at just 0:35 of round one due to a guillotine choke after attempting a single leg takedown.

Swanson defeated Hiroyuki Takaya via unanimous decision in a bout that earned Fight of the Night honors at WEC 37.

Swanson was scheduled to fight Diego Nunes on the undercard of WEC 40, but Nunes was forced to withdraw from the fight just days before the bout because of a hand injury.

Swanson/Koch was expected to take place on July 2, 2011 at UFC 132.[14] However, Swanson was forced out of the bout with another injury.[15]

After just over a year out of action, Swanson returned to face Ricardo Lamas on November 12, 2011 at UFC on Fox 1, becoming the last WEC fighter imported from the WEC/UFC merger to debut in the UFC.[16] He lost the fight via submission (arm triangle choke) in the second round.

Swanson faced Ross Pearson on June 22, 2012 at UFC on FX 4.[18] He won the fight via TKO in the second round, earning the Knockout of the Night bonus.

Swanson faced Charles Oliveira on September 22, 2012 at UFC 152.[19] Early in the first round, Swanson hit Oliveira with body (liver) shot, which visibly appeared to hurt Oliveira. Swanson followed it up with an overhand right sending Oliveira to the canvas resulting in a KO victory for Swanson.[20] Swanson received a $65,000 bonus for Knockout of the Night.[21]

Swanson's bout with Dennis Siver was rescheduled for July 6, 2013 at UFC 162.[24] After a back and forth first two rounds, Swanson defeated Siver via TKO due to punches in the third round. The performance earned both participants Fight of the Night honors.

Swanson faced Jeremy Stephens on June 28, 2014 at UFC Fight Night 44.[25] Swanson won the fight via unanimous decision. The performance earned both participants Fight of the Night honors.